The present invention relates to a hydrogen generating apparatus, and particularly relates to a hydrogen generating apparatus in which hydrogen is generated by reacting a borohydride fuel with a catalyst.
Recently, as a hydrogen storing material for storing hydrogen, which becomes a fuel of a fuel battery, there has been known a borohydride fuel, which is generated by dissolving a metallic complex compound of NaBH4 and KBH4, etc., in an alkali aqueous solution.
The borohydride fuel is an extremely stable hydrogen storing and supplying material and has a characteristic in which a large quantity of hydrogen is generated under a normal temperature and a normal pressure using a suitable catalyst.
For example, under a following reaction formula, NaBH4 has an ability, when 100% reacted, to generate about 1 liter of hydrogen gas from 1 cc of a fuel of 40 wt %, and this fuel becomes a good fuel for storing hydrogen.
As a prior art technique for generating hydrogen from the borohydride fuel, there is a hydrogen generating apparatus, for example, in which the borohydride fuel is poured into a reactor (a reaction vessel, a processing vessel) in which the catalyst is provided in an interior portion thereof, and then hydrogen is taken out from the borohydride fuel. Such a hydrogen generating apparatus has been known in Japanese patent laid-open publication No. 2002-80202.
The reaction formula of NaBH4 as the borohydride fuel is as follows.NaBH4+2H2O+M+(NaOH)→NaBO2+4H2+M+(NaOH),  (Reaction Formula)
wherein M is a catalyst of a noble metal group, such as platinum and palladium, ruthenium, and magnesium fluoride/nickel hydrogenation, which is made under a low cost and has a high performance hydrogen generating speed.
As stated above, one molecule of NaBH4 and two molecules of water (H2O) for constituting the aqueous solution are catalytically reacted and then hydrogen gas is generated.
Further, at the same time of the hydrogen gas generation, as shown in a right side of the above reaction formula, NaBO2 is generated as a product of the reaction. After a recovery of NaBO2 as a spent fuel, NaBO2 is regeneratively processed to NaBH4 and it can be used again as the fuel.
However, in the conventional hydrogen generating apparatus, for example, when NaBO2 is generated at the same time as the generation of hydrogen from NaBH4 as the borohydride fuel, there is a problem in which NaBO2 adheres to the catalyst in the reactor, and thereafter the reaction slows and there occurs a danger that hydrogen is not taken out safely after a period of operation.